Overload reset circuit



Sept. 29, 1953 H. F, MAYER 2,654,052

OVERLOAD RESET CIRCUIT Filed Aug. 27, 1951 Z2 n Z5' -fZiL/Ar. f

. INVENTOR.

Patented Sept. 29, 1953 OVERLOAD RESET CIRCUIT Harry F. Mayer,Baldwinsville, N. Y., assignor to the United States of Am the Secretaryof the Air Application August 27, 1951, Serial No. 243,897

3 Claims.

The invention described herein may be manufactured and used by or forthe Government for governmental purposes without payment to me of anyroyalty thereon.

This device relates to overload re-set circuits which have for theirfunction the removal of primary power from a load upon the occurrence ofan overload and which will restore the power after a predetermined timeinterval.

One object of the invention is to provide a circuit of the classdescribed, which is especially adapted to radar modulators and otherkinds of electronic equipment. Heavy currents such as are necessary tooperate re-setting overload circuit-breakers are not necessary for thiscircuit.

Another object of the invention is to provide a device of the abovecharacter iny which the resetting time delay is adjustable over widelimits.

In radar modulators and in many other types of electronic equipmentoverload is apt to occur due to occasional intermittent malfunctioningof a tube in the load circuit. For example, the thyratron in themodulator may arc back, or may fail to extinguish after a pulse; or themagnetron load may spark over. Any of these occurrences will causeexcessive current to 4be drawn from the rectier which supplies thepower. It is common practice to include a current-sensitive faultresponsive relay in the output circuit of the rectier, connected so asto interrupt primary power` when the output current exceeds a certainvalue. If the relay returns to its normal position when the primarypower is removed and the output current falls to zero, then primarypower is immediately re-a'pplied. This happens so quickly that generallythe malfunctioning which caused the overload will continue, and therelay will oscillate rapidly, turning power on and oi to no avail.

An alternative is to use a holding circuit which will cause the primarypower to stay oil when interrupted by an overload, until a manual resetswitch is operated. This is satisfactory in some applications, but notin others. In particular, it is not satisfactory in a re control radarsystem, where the necessity for operating the re-set switch in themiddle of a shooting engagement would be disastrous.

The circuit here described removes the primary power, waits apredetermined time (adjustable over wide limits, but for application toradar sets xed at approximately 1A? second), and then restores primarypower.

With reference to the drawing, the reference numerals I and 2 designateconductors in a primary alternating power circuit such as the input tothe power rectifying equipment of a radar set erica as represented byForce and connected in series by the normally closed contacts 3 and 4,the latter contact being mounted on the movable armature 5 of a circuitbreaking relay generally indicated at 6. The coil 'I of the relay E hasone terminal grounded and the other terminal connected by conductor 8 tothe lower contact 9 of an overload control relay generally indicated bythe reference numeral I5.

The armature I of relay I5 is connected to a suitable source of D. C.potential such as 28 volts and normally engages the lower contact 9 whenthe relay I5 is de-energized- Current from the 28 volt source thusnormally ows to ground through the coil I of relay 6 maintaining therelay energized and primary circuit breaking contacts 3 and 4 normallyclosed.

The relay I5 has an upper contact II connected by means of a resistor I2and conductor I3 to one terminal of a holding coil I4 the other terminalof which is grounded. When the relay armature itl engages contact II theholding coil is energized with direct current from the 28 volt sourcewhich is reduced across resistor I 2 to about 20 volts D. C.

The relay I5 is also provided with a coil IB connected in series withconductors I'I and I8 of the load circuit to be protected such thatcurrent overloads through the coil I6 activate the relay I5 to attractthe armature I D against a suitable biasing force thus energizing theholding coil I4 to maintain the armature in engagement with the uppercontact II until the holding coil circuit becomes de-energized by meanslater to be described. When the armature I0 of relay I5 breaksengagement with contact 9 the relay 8 is de-energized and the relay arm5 drops breaking engagement of contacts 3 and 4 and opening the primarypower circuit which also de-energizes the load circuit.

Means are provided for delaying the de-energizing of the holding coil I4of relay I5 which means comprise a conductor I9 connected to conductor I3 in parallel with the holding coil and which has an adjustableresistance 26 and a capacitance 2I connected in series therewith toground. A conductor 22 connected to conductor I9 between the resistance20 and capacitance 2| is connected to the grid of a conventional triodetype vacuum tube 25. Whenever the relay I5 is activated, current fromthe 28 volt source connected to the armature I0 flows through relaycontact II and resistance I2 to holding coil I4 with a potential ofapproximately 20 volts. This latter voltage is dropped across resistance20 to charge condenser 2I with the charging time being dependent on theRC value of the resistance 20 and capacitance 2I and preferably chosencated at 3e, the other terminator therelay coil.

being connected to a suitabiefhi-'gh 'voltage plate supply. The relay 30has its armature 3l and contact 32 connected to ground `and Vtlieuppercontact 33 connected by means of conductor 34 to conductor i9 above theresistance 23; The contacts 32 and 33 of relay 30 are normally separatedand engaged when relay 370 is energized by `conductance of tube 25 andthe contact engagement .short Icircuits the holding coil I4 and lde--energizes the same.

.From the foregoing it will be apparent that so long :as -the current inthe load circuit I7-I8 and in coil 'IS of relay i5 is below a'predetermined safe vvalue the armature it of the relay will :remain inengagement with the contact 9 permitting current Vfrom, the 28 voltsource Yto :flow through coil 'I of relay e maintaining the sameenergized and keeping the primary power :circuit closed.

Upon occurrence of an overload in the load circuit I'I-Irelay I5 will beactivated to cause the armature ID to engage contact II which willfde-energize relay 6 and open the primary 'power circuit to relieve theoverload by also de-energizing theload circuit. Engagement of the relayvarmature I!) with contact II energizes holding ,coil =I4 to maintainrelay I5 activated and simultaneously will charge condenser 2| at a ratevdetermined 'by the setting of resistance 20.

As the condenser 2I begins to charge the volt- 'a'ge -on the-grid ofvacuum vtube 25 will risemak- -ing the 'grid less negative with respectto the voltage on 'the .cathode and eventually the tube will begin-toconduct current in Vits plate circuit. When the plate current risessuii'iciently, relay 30 will Ibeen'ergized and its contacts32 and 33 inengaging will complete a short circuit of holding coil I4 causing relayvI5 to drop out and relay 6 to becomelactive .to again close the powercircuit. l

When'relay 30 becomes energized and its contacts 33 and 34 short circuitthe holding coil I4 of relay "I the charge on condenser 2l is dischargedto ground and the bias voltage'on the cathode of tube drivesy'the"tube25 -to cut-01T, rie-energizing the plate circuit and relaywhich in dropping out, removes the Vshort circuit on holding lcoil *IILrestoring initial conditions.

Tf `the overload condition persists, the vabove cycle of operations willbe repeated with the primarycircuit'being opened for a one-'half secondperiod during each cycle of the overload protectivev system.

Having now described the invention what I desire to "protect by UnitedStates Letters Patentis dened in the appended claims.

I claim:

l. A protective arrangement fora power lcircuit comprising afault-responsive relay having a first set of contacts, means responsiveto the closing of the rst set of contacts for closing said powercircuit, a second set of contacts closed when said first set of contactsis open, means responsive to a fault condition in said power circuit forcausing said rst set of contacts to open and said second set of contactsto close, a holding coil means responsive to the closing of said secondset of' contacts vfor'holding 's aid rst set lof contacts open and saidsecond set ofcontacts closed and means energized in response to clos-:ing of said second set of contacts for de-energizing said holding coilmeans after a predetermined time delay, whereby said second set ofcontacts will/then `be opened and said rst set fof contacts willthen beclosed.

2. A protective arrangement for a power circuit comprising zaVVfault-responsive relay having na Iflrvstlset oi? contacts, meansresponsive to the closing fof the first set of contacts for closing saidpower circuit, a second set of contacts closed when said rst set ofcontacts is open, means responsive to a fault condition in said powercircuit for causing said rst set of contacts toy open and said secondset of contacts to close, holding coil means responsive to the closingof said second set of contacts for holding said rst set `of contactsopen and said second set of contacts rclosed and means 'including anelectronic discharge device Lhaving at least an anode, a cathode and acontrol grid, which device is normally Anon-conducting and meansincluding an adjustable resistor and condenser for applying a potentialto the control grid of said electronic discharge device and saidpotential being of sufcient value to cause said electronic dischargedevice yto be made conducting `in :response `to the ciosing ofsaid'second set vof contacts andmeans responsive to the conductivity ofsaid electronic discharge device for de-energizing said holding coilmeans.

3. A protective arrangement for a power circuit comprising afault-responsive relay having a rst winding, a second winding, va firstset of contacts closed in the non-operative condition ofthe relay and asecond set of contacts closed in :the operated condition of the relay,and an electromagnetic `power-controlling relay having contacts`controlling the flow of power in said `power circuit, said contactsYbeing normally open and closed when said electromagnetic'powercontrolling relay isenergized, circuit means including said rstset of contacts for Yenergizing said lelectromagnetic power-controllingrelay, circuit means including said second set ofvcontacts forenergizingsaid second winding, circuit means including a resistor and a condenserfor producing Va Voltage which increases as a function of time, and anelectronic discharge device having at least an anode, a cathode and acontrol grid, circuit means for applying said voltage to said controlgrid, and an anode-cathode circuit `for said electronic discharge deviceincluding an electromagnetic relay having an energizing winding,contacts controlled by said electromagnetic relay and circuit means forshort circuiting said second winding when said contacts are closed.

HARRY F. MAY-ER. l

:References lCited 'in the le of this patent 'UNITED STATES PATENTSNumber Name Date I 2,451,953 Ingram Oct. 19, 1948 2,473,344 yMcCown June14, 1949 2,527,483 Klemperer Oct. 24, C)

